Robotic systems are often used in applications that require a high degree of accuracy and/or precision, such as surgical procedures or other complex tasks. Such systems may include various types of robots, such as autonomous, teleoperated, and interactive. This disclosure is directed towards interactive robotic systems with haptic control.
Interactive robotic systems are preferred for some types of surgery, such as joint replacement surgery, because they enable a surgeon to maintain direct, hands-on control of the surgical procedure while still achieving a high degree of accuracy and/or precision. For example, referring to FIGS. 1-3, in hip replacement surgery, a surgeon can use an interactive, haptically guided robotic arm equipped with a semi-spherical cutting tool or cutting tool 23 in a passive manner to sculpt a semi-spherical indentation in the acetabulum 21, which is a cup-shaped socket in the pelvis 22. The acetabulum 21 receives a cup commonly referred to as an acetabular cup (not shown) that, in turn receives a resurfaced femoral head in a partial hip arthroplasty or, in the case of a total hip arthroplasty (THA), the ball portion of the hip implant. To sculpt bone or, in this example, the portion of the acetabulum 21 where the cup is to be located, the surgeon manually grasps and manipulates the robotic arm 20 to move a cutting tool or cutting tool 23 that is coupled to the robotic arm. As long as the surgeon maintains the cutting tool within a predefined virtual cutting boundary defined by a straight line haptic path, the surgeon can move the robotic arm freely with low friction and low inertia. However, if the surgeon attempts to move the cutting tool to cut bone off of the haptic path, the robotic arm provides haptic (or force) feedback that prevents or inhibits the surgeon from moving the cutting tool beyond the virtual cutting boundary.
In other types of surgeries, haptic volumes are used instead of straight-line haptic paths. For example, as disclosed in commonly assigned US2006/0142657, haptic volumes having various geometric volumes may be modeled using planes, spheres, cones, cylinders, etc.
Returning to hip replacement surgeries, such as THAs, surgical robotic tools are typically limited haptically to a straight line path, normal to where the rim of the planned cup will be after installation or possibly offset a known distance from the planned central axis of the acetabular cup. The semi-spherical cutting tool 23 that is extended along a straight line results in a reamed volume that is cylindrical in shape, except at the semi-spherical end. The intention of a straight line haptic path is to constrain the center of the semi-spherical cutting tool 23 along a path that is normal to the rim of the planned acetabular cup and to provide a semi-spherical reamed end for receiving the cup. To avoid unintended reaming and inaccurate bone preparation, if the center of the cutting tool 23 is not maintained along the straight line haptic path, the controller may not allow the cutting tool 23 to operate.
The above-described interactive robotic system, though useful for THA, is not optimally suited for THA and other types of replacement surgeries that require the use of multiple surgical tools having different functions (e.g., reaming, impacting), different configurations (e.g., straight, offset), different sizes (e.g. multiple cutting tools of different sizes) and different weights. A system designed to accommodate a variety of tools may be prohibitively complex for haptic control because it would require removing and attaching different types of tools to the robotic arm during a surgical procedure which may affect the accuracy of the haptic path and could increase the time needed to perform the procedure.
Further, in THA, in addition to maintaining an appropriate cutting boundary, an angular orientation of surgical tools and implants is important. For example, in conventional THA, the surgeon uses the semi-spherical cutting tool 23 (FIG. 2) to resurface the acetabulum 21 (FIG. 1). Then, an acetabular cup is attached to a distal end of an impactor tool (not shown). The surgeon implants the acetabular cup into the reamed socket by repeatedly striking a proximal end of the impactor tool with a mallet. Angular orientation of both the reamed socket and the implanted acetabular cup is important because incorrect orientation can result in misalignment of the acetabular cup away from the appropriate version and inclination angles of the acetabular anatomy. Misalignment can lead to post-operative problems, including joint dislocation, impingement of the femur on the acetabular cup at extreme ranges of motion, and accelerated wear of the acetabular cup due to improper loading of the femoral head-to-acetabular cup interface. Alignment is also important to maintain correct leg length and medial/lateral offset. Even more problematic, recent advances in THA reveal that the ideal acetabular cup position is in a narrower range than previously appreciated and that acetabular cup position is dependent on femoral component anteversion.
Use of a straight line haptic path or straight line reaming does not allow for a single-stage reaming process in most cases. Specifically, the surgeon typically uses cutting tools of different sizes in order to achieve the correct size and orientation for the acetabular cup. Single stage reaming is desirable because it is fast, reduces the possibility of infection and reduces operating room time. However, a straight line haptic path is not possible, for example, if the tool center is pushed away from the haptic path by the surface of the acetabular rim. Because the center of the cutting tool is pushed off the haptic path in these cases, before the bowl-shaped indentation for the cup is reamed, the surgeon is required to employ multi-stage reaming with different cutting tools or ream free-handed without the benefits of haptic constraint.
For at least these reasons, more accurate acetabular cup positioning techniques will be important because it is well known that misalignment of the acetabular component in THA may result in dislocation, reduced range of motion or accelerated wear. Further, improved haptic control systems for hip replacement and other surgeries are needed that afford the surgeon some additional flexibility while still employing haptic control.